**1. Introduction**

For the past decade, the use of biopolymers materials instead of conventional and highly polluting materials, has increased substantially. Biopolymers can be obtained from various sources; the most used are those based on polysaccharides (sodium alginate, agar, chitosan, carrageenan, starch and cellulose), lipids (waxes and fatty acids) and proteins (gelatin, collagen and soy protein isolate) [1]. They are extensively used, owing to the properties of biobased materials, such as mechanical performance, physicochemical characteristics comparable to those of conventional materials [2], antibacterial and antioxidant properties, high biocompatibility, compostability, non-toxicity, non-immunogenicity, non-carcinogenicity, and non-inflammatory and non-allergenic character [3,4]. Multiple manufacturing methods have increased their widespread use. They can be used for the

**Citation:** Gheorghita Puscaselu, R.; Lobiuc, A.; Sirbu, I.O.; Covasa, M. The Use of Biopolymers as a Natural Matrix for Incorporation of Essential Oils of Medicinal Plants. *Gels* **2022**, *8*, 756. https://doi.org/10.3390/ gels8110756

Academic Editors: Aris E. Giannakas, Constantinos Salmas and Charalampos Proestos

Received: 19 October 2022 Accepted: 19 November 2022 Published: 21 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

development of films or coatings, capsules, gels or hydrogels. Owing to their matrix, which has a compact structure and high retention capacity, they can be enriched by the addition of various biologically active substances. Furthermore, they are environmentally friendly, completely edible and produce zero waste after use [5].

Essential oils (EOs) have been used since ancient times, owing to their health benefits and sensory and antioxidant properties. Thus, essential oils, such as those extracted from medicinal plants, contain active compounds, such as limonene, pinene, myrcene (orange, lemon, grapefruit and chamomile) [6,7], eucalyptol, eugenol, gingerol, and cedrene (ginger, cinnamon, clove and mint) compound [8], with beneficial effects on the human body. Thus, orange, lemon and ginger EOs have been used for their relaxant effect or pain relief [9,10], whereas grapefruit, cinnamon and mint EOs have been used for their anti-inflammatory, antimycotoxigenic, antitumoral and antigenotoxic effects [11–13]. In medicine, lemon EO has been used to relieve the symptoms of gastrointestinal diseases and depression [14]; ginger EO has been used for sore throat, cough, cold, dyspepsia, gastritis and gastric ulcerations [15]; clove EO has been used for urinary tract infections, digestive disorders, athlete's foot disease, in dentistry and as a kidney tonic [16,17].

Several studies have demonstrated the positive effects of the use of essential oils, for example, in preventing infection with the SARS-CoV-2 virus. Senthil Kumar et al. [18] showed that lemon essential oil, through its compounds, such as citronellol, geraniol, and neryl acetate, was capable of preventing replication of coronaviruses by blocking the entry of the virus into the host cells through downregulation of ACE2 receptor expression in epithelial cells.

Owing to their benefits and consumers predisposition toward products that are as natural as possible, research in the field has been oriented towards the development of innovative materials obtained from renewable resources. Thus, materials based on biopolymers with incorporated essential oils have been developed. Initially, they were used in the food industry to improve the sensorial quality or to increase the shelf life of various food products, such as those based on meat or fish [19–22], fruits or vegetables [23–25], sweets [26,27], beverages [28] or dairy products [29,30]. Later, they were added to increase the nutritional value and bioavailability of products, especially those with beneficial effects on health. Thus, numerous essential oils, such as those from citrus fruits (lemon, orange and grapefruit) or medicinal EOs (ginger, chamomile, mint, eucalyptus, cinnamon or cloves) have been incorporated into biopolymeric materials. However, the development, characterization and testing of these films under various experimental conditions using several well-known plant-based oils with applicability in biomedical, cosmetic or food industries are still needed. Therefore, in this study, we tested biofilms incorporated with two concentrations (7.5% and 15%, *v*/*w*) of essential oils of lemon, orange, grapefruit, cinnamon, clove, chamomile, ginger, eucalyptus or mint at the time of development and after one year of storage under normal temperature and humidity conditions.
